A friend of mine in CO has a Wilson Glock19 and a Shadow systems DR920 and a Glock19.4 with a Timney trigger. I do not have a Shadow systems gun, and have never shot one (I had heard great things about them though).
The first thing he did when he bought the Shadow systems gun was go out and shoot it and it jammed on him about 1:10 rounds. He called Shadow systems and spoke to the LGS (where he bought it) and they were very adamant that he had to run 200 rounds through it "before it would function reliably". So he kept shooting it and noticed the coating on the barrel was being scraped off. He called them again and they sent him a new barrel free of charge. He installed it and headed to the range.
He shot about 100 rounds through it and took it apart and cleaned it. No Jams and no barrel coating damage. He liked it>
He took it out last week and it jammed 1:20 rounds right off. He could pop the back of the slide and it would feed and he could continue. He shot 150 rounds and no change, it continued to jam. He took it apart, no apparent problems, cleaned it, oiled it and went out again over the weekend with the same result. The LGS sold him some type of lubricant and Shadow Systems told him to send the gun in for them to take a look at it.
He loves the Wilson, and his gen4 19. He has never had a failure to feed with either of them (nor have I had any failures with any of my Glocks). He is really disappointed in the Shadow Systems, and while he is pretty confident they will fix whatever is wrong with it, he does not like the 4 to 6 week turnaround time he was promised. He started competing in some local club matches and the Shadow Systems weapon was bought specifically to run those matches.
I have shot a couple of Zev's guns and they seem nice, but they do not feel different or perform better than the 100% reliability of the Glocks I have. I understand the grip on the Shadow systems is different than Glock (angle) and my friend really likes the feel of it. But as for me, on my Glocks, I have changed the sights, changed the triggers, lapped the slide rails and mounted an RMR on my G45 - 100% reliable and seem to run as smooth as a striker fired can so while the rep for the Shadow systems gun is good over all, is it really that much better than G45.5 with new sights and RMR? I do not expect it to be STI smooth, but my guns seem to run pretty darn smooth...so what is "better" about the Shadow Systems guns (or the Zev for that matter) that I am missing?